Well, I sent John's reply to the person who originally pointed out that
he thought the OM Dioptric Correction lens table is wrong. Below are
his comments in return. I'm leaving David's name and email on this, in
case any of you who have dealt with this problem want to contact him
privately. I don't wear glasses (vision 20/10 at last check :), but I
do want the table in the FAQ to be correct, if in fact it is not
currently correct. If anyone has any bright ideas, let me know :)
Cheers,
--Lee
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Message-ID: <003e01bfe11a$d4473920$6a75d7d8@lazaroff>
From: "David W. Lazaroff" <lazaroff@xxxxxxxxx>
To: "R. Lee Hawkins" <lhawkins@xxxxxxxxxxxxxxxxxxxxxxxxxx>
Subject: Re: Information in error
Date: Wed, 28 Jun 2000 09:05:18 -0700
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Lee,
Thanks for forwarding the letter, but I'm afraid it doesn't help.
I already know with certainty the actual value of dioptric correction lens I
need (+1 diopter) because I've tried looking through the viewfinder using
reading glasses of different strengths. The problem is figuring out what
nominal value of Olympus dioptric correction lens corresponds to an actual
value of +1 diopters. The table that appears on your website and elsewhere
on the Internet doesn't show the correspondence accurately, so the only way
I can find the right correction lens is to try several and choose the one
that works best.
In case it helps to clarify things for you and John, I'll respond to some of
the things he wrote.
>It is my understanding the diopter correction used should be from the
>"distance" prescription, not the one for "reading" (close focus) lenses.
>This would be in line with dioptric correction for other makes of
>cameras.
Yes, if what he means by the "distance" prescription is a prescription for
comfortably viewing things not at infinity, but at a distance of a couple of
meters.
>The appparent distance of the focus screen and display in the viewfinder is
>on the order of at least several feet (4-6 feet; 1-2 meters).
It's about 2m in my OM-2N. I measured it.
>I think it
>would be rare that someone would need "reading" or close focus correction
>at that distance.
Maybe so, but the fact is that I need a correction of +1 diopter to view
things at that distance.
>This would make sense in design to keep the apparent
>distance beyond the range of close focus issues for those (like me) who
>have to use reading lenses.
Sure, but the apparent distance isn't beyond the range of close focus issues
for me.
>I also wear distance glasses and with the
>OM-1n there is no problem viewing the focus screen as long as I am wearing
>them.
Of course, I can see the focus screen clearly with with +1 corrective
glasses. But with glasses on I can't get my eye close enough to the
viewfinder window to see the entire focusing screen. That's why the
equivalent dioptric correction lens would be preferable.
>Question for the individual who asked about the table: does he (she) wear
>corrective lenses for "distance" or only for reading? What is _that_
>prescription?
I wear +1 diopter corrective lenses for viewing things at a distance of
about 2m, as in an art museum. I wear +2.5 diopter corrective lenses for
reading books.
>I suggest trying the closest dioptric correction lens from
>the table for that prescription (prescription-2 diopters as the table
>states).
That's exactly what I tried. I started with the value of the lens I need, +1
diopter, which John calls my "distance" prescription. Going by the tabIe, I
subtracted 2 from it, and ordered a lens with the nominal value -1 (negative
1), believing that lens would have an actual power of +1 diopter. It turned
out instead to be a weak negative lens, with an actual power of about - 0.3
(negative 0.3). In other words, the table was wrong. The table is the whole
problem.
>BTW, the other way to get dioptric correction is to take a lens from a pair
>of old glasses having the same _distance_ (not reading) correction as the
>current prescription and have a dioptric correction lens cut from the
>middle of it. This requires that the eyecup allows replacing the lens in
>it.
Yes, this is an old trick. I could buy an eyecup that accepts replaceable
correction lenses and have a little disk cut from +1 reading glasses. That
would be a nuisance, made worse by the fact that lenses in glasses tend to
be considerably thicker than the lenses for which eyecups are designed.
David
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